1. Field of the Invention
The present invention relates generally to an oil-hydraulic control device for selectively operating plural kinds of oil-hydraulic actuators and, more particularly, to an oil-hydraulic control device for selecting a specific oil-hydraulic cylinder to be operated from among plural kinds of oil-hydraulic actuators by a selective valve, extending and retracting it by a directional control valve and extending it quickly by a quick extensional valve.
2. Related Technology and Prior Art
One of the inventors of the present invention has already proposed the No. 1 related technology Japanese Provisional Utility Model Publication No. 60-154454) as shown in FIG. 10 for the construction to operate selectively plural kinds of oil-hydraulic actuators in the above-mentioned oil-hydraulic control device.
This technology can be used for operatively driving a front loader equipped as a attachment to an agricultural tractor, and is intended to simplify the detachable connection between two oil-hydraulic cylinders and oil-hydraulic hoses by reducing the number of the hoses from four originally required to two when the front loader is equipped with detachably to the tractor. Further, in spite of requiring four long pipes for actuators used for a working attachment provided remotely from a control cab in a tractor, it is intended to manage with two pipes.
The construction according to the No. 1 prior technology is as follows. That is, an arm cylinder 105 and a bucket cylinder 106 are adapted to be selectively connected to an oil-hydraulic pump 101 through a directional control valve 102, a self-sealing coupling 103 and an actuator selective valve 104 arranged in series thereto. The operative cylinder is selected from both cylinders 105,106 by the actuator selective valve 102. And then the selected cylinder 105 or 106 is operated extendedly or retractedly by the directional control valve 102.
Further, in the oil-hydraulic control device there is provided the No. 2 technology of the prior art Japanese Utility Model Publication No. 59-34721) as shown in FIG. 11 wherein disclosed is the construction to extend the oil-hydraulic cylinder quickly by a quick extensional valve.
This technology is intended to perform quickly the dump operation of the bucket of the front loader, and has the construction as follows. That is, the quick extensional valve 201 functions to retract the cylinder 202 at a normal speed when the valve 201 is returned to a returned position 204 by a returning spring 203 in the case of retracting the cylinder 202. To extend the cylinder 202 quickly, the valve 201 is switched to a quick extensional position automatically by a pilot pressure in a pilot oil passage 205 for extending the cylinder 202. At the begining of the extensional operation of the cylinder 202, when the introduction of the pressure oil into the bottom side oil chamber 207 thereof is started, the return oil from the head side oil chamber 208 changes over the quick extensional valve 201 from the retractive position 204 to the quick extensional position 206 with the pilot pressure passing through the pilot oil passage 205 due to a pressure difference generated at either side of the throttle 212 by the return oil passing through the throttle 212. Then, the return oil from the head side oil chamber 208 is supplied to the bottom side oil chamber 207 through the by-pass 209 in the quick extensional position 206. Hence, the pressure oil introduced into the bottom side oil chamber 207 from the oil-hydraulic pump drives the cylinder 202 operatively so as to be extended quickly according to the following expression. EQU V.apprxeq.Q/A
V; extending speed of the cylinder 202 PA1 Q; flow of the pressure oil PA1 A; sectional area of the piston rod 210.
On the other hand, it is readily thought that the quick extensional valve device 211 of the No. 2 prior technology shown in FIG. 11 can be combined with the No. 1 technology as shown by the dot-dash line in FIG. 10. This combined construction has advantageously both merits of the No. 1 technology and the No. 2 technology, but still has the following problems. That is, (A) The quick extensional valve 201 and a special oil pressure circuit for changing over the valve 201 automatically are needed additionally. (B) During the normal speed operation except a slow speed operation regulated by the throttle 212 when the cylinder 202 is extended, since the quick extensional valve 201 always operates automatically for the cylinder 202 to be extended quickly, it becomes impossible to perform the powerful extensional operation thereof at a normal speed.